Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase
E. Wolarza, D. Baumana, J. Jadżynb and R. Dąbrowskic
aFaculty of Technical Physics, Poznań University of Technology, Nieszawska 13a, 60-965 Poznań, Poland
bInstitute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland
cInstitute of Chemistry, Military University of Technology, S. Kaliskiego 1, 00-950 Warszawa, Poland
Received: September 20, 2010; In final form: April 28, 2011
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Dielectric relaxation study of nematogenic 4-n-alkyl-4'-cyano-bi-phenyls (nCB, n = 5, 6), 4-(trans-4'-n-alkyl-cyclo-hexyl)isothio-cyanato-benzenes (nCHBT, n = 6, 8), 4-cyano-phenyl-4'-n-alkyl-benzo-ates (nCPB, n = 6, 8), 4-cyano-3-fluoro-phenyl-4'-n-octyloxy-benzoate (8OCFPB), and 4-cyano-phenyl-4'-n-octyloxy-3'-fluoro-benzoate (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier-Saupe-Martin model of molecular diffusion in nematics, the orientational order parameter 〈 P2 〉 was determined from dielectric relaxation times and retardation factor. The values of 〈 P2 〉 calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional effect and the orientational order in the nematic phase were discussed.
DOI: 10.12693/APhysPolA.120.447
PACS numbers: 42.70.Df, 61.30.Gd, 77.22.Ch